Boffins propose photon-swapping entanglement experiment on ISS

Spooky in space

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Hard on the heels of a Chinese claim to have measured the speed at which entanglement can transfer information, a group led by Austrian Academy of Sciences professor Rupert Ursin proposes testing “spooky action's” speed between Earth and the International Space Station.

The researchers note that the only kit required on the orbital platform would be a photon detector, which they say could be installed on an existing ground-facing Nikon 400mm camera in the ISS's Cupola module.

The “Bell experiment” would involve testing the entanglement of pairs of photons generated on the ground, one of which would be sent to the ISS. Measuring the state of the earth-bound photons should, if they are truly entangled, determine the state of the photon detected in space.

Since the experiment is probabilistic, you need lots of measurements to tell the difference between coincidence and entanglement. Any individual test of two photon's characteristic (for example, measuring their polarisation) might be the result of chance.

However, as the researchers point out, there are times of the year where the ISS makes five or six passes in succession, all with the right orientation to carry out an experiment. For each pass, they propose a 70-second experiment.

“We envision setting up the experiment for a whole week, and therefore having more than enough links to the ISS available”, professor Ursin says in Phys.org.

A successful experiment would demonstrate entanglement at a distance of 500 km, which Ursin says is far further than any Earth-bound entanglement experiment has achieved. The experiment would also help investigate whether gravity has any affect on entanglement between a photon on Earth and on in orbit.

A second experiment, arguably with more immediate practical application, will test quantum key distribution between Earth and the ISS.